This invention relates generally to a sheet guide and driving apparatus and more particularly, concerns a pretransfer device to guide a sheet to a transfer zone on a photoreceptive member while causing a minimal disturbing force to the photoreceptor and the image developed thereon by the sheet.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
The foregoing generally describes a typical black and white electrophotographic printing machine. With the advent of multicolor electrophotography, it is desirable to use an architecture which comprises a plurality of image forming stations. One example of the plural image forming station architecture utilizes an image-on-image (IOI) system in which the photoreceptive member is recharged, reimaged and developed for each color separation. This charging, imaging, developing and recharging, reimaging and developing, all followed by transfer to paper, is done in a single revolution of the photoreceptor in so-called single pass machines, while multipass architectures form each color separation with a single charge, image and develop, with separate transfer operations for each color.
In single pass color machines it is desirable to cause as little disturbance to the photoreceptor as possible so that motion errors are not propagated along the belt to cause image quality and color separation registration problems. One area that has potential to cause such a disturbance is when a sheet is released from the guide after having been brought into contact with the photoreceptor for transfer of the developed image thereto. This disturbance which is often referred to as trail edge flip can cause image defects on the sheet due to the motion of the sheet during transfer caused by energy released due to the bending forces of the sheet. Particularly in machines which handle a large range of paper weights and sizes it is difficult to have a sheet guide which can properly position any weight and size sheet while not causing the sheet to oscillate after having come in contact with the photoreceptor.
It is therefore desirable to have a pretransfer sheet guide that can handle a wide variety of sheet weights and sizes while maintaining the capability to align and deliver the sheet to the photoreceptor with as little impact and sheet motion as possible.
In accordance with one aspect of the present invention, there is provided a sheet feeding device for moving a sheet along a path, comprising a first drive nip and a substantially frictionless baffle adjacent said first drive nip, said baffle further including a plurality of control members to induce a predetermined bend to a sheet and to deliver the sheet at a predetermined point at a specific alignment and a trail edge guide member to maximize the effective beam length of a sheet contacting said trail edge guide and a photoreceptive member.
In accordance with another aspect of the invention there is provided an electrophotographic printing machine having a photoreceptive member and including a pretransfer sheet feeding apparatus, comprising a first drive nip and a substantially frictionless baffle adjacent said first drive nip, said baffle further including a plurality of control members to induce a predetermined bend to a sheet and to deliver the sheet at a predetermined point at a specific alignment and a trail edge guide member to maximize the effective beam length of a sheet contacting said trail edge guide and a photoreceptive member.